This invention relates to color projection systems, and more particularly relates to such projection systems incorporating a single electro-optical light modulator.
Color projection display systems are known in which a white light source is separated into red, blue and green sub-beams for separate modulation by corresponding color components of an incoming display signal, and then the modulated subbeams are recombined into a full color display for projection onto a viewing screen. Modulation of the subbeams is commonly carried out using three separate electro-optical light modulators such as liquid crystal display (LCD) panels, one for each of the three subbeams.
However, in one type of color projection system, described for example in U.S. Pat. No. 5,532,763, the three subbeams are all modulated by a single LCD panel. This is accomplished by shaping the subbeams into band-shaped cross-sections, and scrolling the bands sequentially across the LCD panel, while synchronously addressing those portions of the panel which are illuminated by the bands with the corresponding display signal information. Such projection systems are referred to herein as single panel scrolling raster (SPSR) projectors.
The simultaneous use of a substantial portion of the available red, blue and green light through a single light valve panel provides optical efficiencies comparable to that of three-panel systems employing the same types of light-valve panels. Using only a single panel eliminates the need to mechanically converge different color images, formed on different panels, and reduces system cost.
Various scrolling means for such SPSR systems are disclosed in U.S. Pat. No. 5,548,347. A system employing single-prism scrolling means is simple and compact, while multiple-prism (either separated or physically joined) scrolling means offer better scroll-speed uniformity (for the different color light bands) and scroll-speed linearity (for each light band) than the single-prism system. A system employing three physically separate prisms located in separate light paths, as shown in FIG. 16 of the patent, offers better optical efficiency than a system employing three physically joined prisms, but is less compact.
A disadvantage of all such SPSR systems is the requirement for a relatively large LCD (having at least an approximately 1.3 inch diagonal for current lamp technology), in order to accept the light from the three separate primary color beams. Such large LCDs are expensive, and require the use of comparatively large, expensive optical components.